I. Field
The subject technology relates generally to communications systems and methods, and more particularly to systems and methods that enhance receiver performance in a wireless system by exploiting multiple antennas at the receiver.
II. Background
One technology that has dominated wireless systems is Code Division Multiple Access (CDMA) digital wireless technology. In addition to CDMA, an air interface specification defines FLO (Forward Link Only) technology that has been developed by an industry-led group of wireless providers. In general, FLO has leveraged the most advantageous features of wireless technologies available and used the latest advances in coding and system design to consistently achieve the highest-quality performance. One goal is for FLO to be a globally adopted standard.
The FLO technology was designed in one case for a mobile multimedia environment and exhibits performance characteristics suited ideally for use on cellular handsets. It uses the latest advances in coding and interleaving to achieve the highest-quality reception at all times, both for real-time content streaming and other data services. FLO technology can provide robust mobile performance and high capacity without compromising power consumption. The technology also reduces the network cost of delivering multimedia content by dramatically decreasing the number of transmitters needed to be deployed. In addition, FLO technology-based multimedia multicasting complements wireless operators' cellular network data and voice services, delivering content to the same cellular handsets used on 3G networks.
The FLO wireless system has been designed to broadcast real time audio and video signals, apart from non-real time services to mobile users. The respective FLO transmission is carried out using tall and high power transmitters to ensure wide coverage in a given geographical area. In a broadcast Orthogonal Frequency Division Multiplexing (OFDM) system such as FLO, respective OFDM symbols are organized into frames having physical layer packets that are encoded with a Reed-Solomon (R-S) code and distributed across the frames to exploit time-diversity of a fading channel. Time diversity implies that several channel realizations are observed over the duration of each code block and hence, the packets can be recovered even if there was a deep fade during some of the packets. However, for very low speeds of a mobile handset or receiver (small Doppler spread), the channel coherence time is long compared to the time-span of a Reed-Solomon code block and thus, the channel evolves slowly. As a result, little time-diversity can be gained within a Reed-Solomon code block (for FLO, a Reed-Solomon code block spans across four frames. As a result, the duration of a Reed-Solomon code block is approximately 0.75 second). The prior approach was to use a single receive antenna on the handset. However, as the speed of the mobile handset (or Doppler spread) changes, especially for low Doppler spread scenarios, the performance of single receive antenna FLO receiver architectures can degrade.